Display screen or portion thereof with a transitional graphical user interface



FIG. 1 is an enlarged front view of a first image in a sequenceaccording to a first embodiment of my design for a display screen orportion thereof with a transitional graphical user interface;

FIG. 2 is an enlarged front view of a second image in the sequencethereof;

FIG. 3 is a front view of a first image in a sequence according to asecond embodiment of my design for a display screen or portion thereofwith a transitional graphical user interface; and,

FIG. 4 is a front view of a second image in the sequence thereof.

The appearance of the transitional image transitions between the imagesshown in FIGS. 1-2 and 3-4. The process or period in which one imagetransitions to another forms no part of the claimed design.

The long dash broken lines show an electronic device for the purpose ofillustrating environmental structure and form no part of the claimeddesign. The dash-dot-dash broken lines show portions of the graphicaluser interface and form no part of the claimed design. The dash-dashbroken lines show a display screen or portion thereof and form no partof the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha transitional graphical user interface, as shown and described.